Binocular calibration target

ABSTRACT

A system for providing two parallel light beams spaced-apart a selectable distance, the system including: a first beam splitter configured for reflecting a light beam from a light source to create a first datum light beam, the first beam splitter is fixedly attached to a base; a second beam splitter configured for reflecting a transmitted light beam from the light beam from the light source to create a second datum light beam, a third beam splitter configured for reflecting a transmitted light beam from the light beam from the light source to create a third datum light beam, a fourth beam reflecting device configured for reflecting a transmitted light beam from the light beam from the light source to create a fourth light beam. Each of the second, third beam splitters and fourth beam reflecting device is configured to be slidingly attached to the base.

PRIORITY CLAIM AND RELATED APPLICATIONS

This divisional application claims the benefit of priority fromnon-provisional application U.S. Ser. No. 17/683,295 filed Feb. 28,2022. Said application is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION 1. The Field of the Invention

The present invention relates to a calibration system for a pair ofbinoculars. More specifically, the present invention is directed to adatum-based expandable calibration system for a pair of binoculars.

2. Background Art

Product performance testing of a pair of binoculars, e.g., AugmentedReality/Virtual Reality (AR/VR) glasses requires the use of perfectlyparallelly-disposed light beams received at the entrance pupils of theglasses to simulate a pair of human eyes. A deviation or defect of anyone of the light paths through the entrance pupils of the glasses issufficient to cause severe discomfort to a user of the glasses. Thegenesis of a deviation of a light path through an entrance pupils ofAR/VR glasses can be imperfections introduced during fabrication,shipping and/or use of the AR/VR glasses. During a quality controlprocess, a calibration system may be used in conjunction with theglasses to calibrate the glasses by indicating a deviation and adjustingone or more light paths of the glasses to eliminate the deviation.However, for the calibration system to be effective, the calibrationsystem itself is required to be precise and free from any defects evenwhen the interpupillary distance (IPD) of the calibration system isadjustable in the range of about 60 mm-220 mm. One such requirement isfor the light beams useful for indicating whether the light pathsthrough the entrance pupils of the glasses are disposed in parallel.Like the glasses themselves, the calibration system useful for thecalibrating the glasses is equally likely to be subject to imperfectionsintroduced during fabrication, shipping and/or use of the calibrationsystem. The interpupillary distance (IPD) of a general adult is betweenabout 60 mm and 75 mm and the image projection module of the glasses isarranged at the outer end close to the human ear and the distancebetween exit pupils is between about 110-135 mm. In some instances, theIPD of the calibration system needs to cover a width of about 60 mm-135mm. In the AR/VR virtual reality display equipment performance detectionprocess, a target source or calibration system with a large IPD and awide object distance range is required. A collimator suitable forproviding large-aperture beams and wide object distances is large andcostly and requires a large space to accommodate it, i.e., a spaceunavailable in a compact calibration system. The distance between theexit pupils of a suitable calibration system needs to be about 60 mm-200mm.

There exists a need for a system for providing a calibration systemhaving two light beams and the IPD of the two light beams must becapable of adjustment such that the distance between the two light beamsis adjustable to coincide with the IPD of the glasses at exit pupils.Further, at least one of the light beams must be capable of adjustmentsuch that the two light beams can be disposed in a perfectly parallelconfiguration.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a system forproviding two parallel light beams spaced-apart a selectable distance,the system including:

-   -   (a) a first beam splitter configured for reflecting a light beam        from a light source to create a first datum light beam and the        first datum beam splitter is configured to be fixedly attached        to a base;    -   (b) a second beam splitter configured for reflecting a        transmitted light beam from the light beam from the light source        to create a second light beam and the second beam splitter is        configured to be slidingly attached to the base; and    -   (c) a collimator configured for directing the first datum light        beam and the second light beam onto an image plane, wherein if a        cast image of the first datum light beam is not coincidental        with respect to the second light beam, the second light beam is        adjusted by at least one of a rotation of the second beam        splitter and a translation of the second beam splitter along the        base such that a cast image of the second light beam coincides        with the first datum light beam, the second light beam is said        to have become a second datum light beam and the first datum        light beam is said to be parallelly disposed with respect to the        second light beam.

In one embodiment, the system further includes a third beam splitterconfigured for reflecting a transmitted light beam from the light beamfrom the light source to create a third light beam and the third beamsplitter is configured to be slidingly attached to the base, wherein thecollimator is further configured for directing the second datum lightbeam and the third light beam onto the image plane, wherein if a castimage of the second datum light beam is not coincidental with respect tothe third light beam, the third light beam is adjusted by at least oneof a rotation of the third beam splitter and a translation of the thirdbeam splitter along the base such that a cast image of the third lightbeam coincides with the second datum light beam, the third light beam issaid to have become a third datum light beam and the second datum lightbeam is said to be parallelly disposed with respect to the third lightbeam. In one embodiment, the system further includes a fourth beamsplitter configured for reflecting a transmitted light beam from thelight beam from the light source to create a fourth light beam and thefourth beam splitter is configured to be slidingly attached to the base,wherein the collimator is further configured for directing the thirddatum light beam and the fourth light beam onto the image plane, whereinif a cast image of the third datum light beam is not coincidental withrespect to the fourth light beam, the fourth light beam is adjusted byat least one of a rotation of the fourth beam splitter and a translationof the fourth beam splitter along the base such that a cast image of thefourth light beam coincides with the third datum light beam, the fourthlight beam is said to have become a fourth datum light beam and thethird datum light beam is said to be parallelly disposed with respect tothe fourth light beam. In one embodiment, the second light beam isdisposed at a perpendicular distance of about 90 mm from the first lightbeam. In one embodiment, the third light beam is disposed at aperpendicular distance of about 90 mm from the second light beam. In oneembodiment, the fourth light beam is disposed at a perpendiculardistance of about 90 mm from the third light beam. In one embodiment,the system further includes at least one shutter to block one of thesecond datum light beam, the third datum light beam and the fourth lightbeam when one of the second datum light beam, the third datum light beamand the fourth light beam is not in use. In one embodiment, the systemfurther includes an image plane configured for receiving an imageresulting from directing the first datum light beam and one of thesecond datum light beam, the third datum light beam and the fourth lightbeam through exit pupils of a pair of binoculars to an entrance pupil ofthe pair of binoculars and if the image is determined to be ofnon-coincidental cast images through the exit pupils of the pair ofbinoculars by the first datum light beam and one of the second datumlight beam, the third datum light beam and the fourth light beam, alight path through a first of the exit pupils of the pair of binocularsis determined to be not parallel to a light path through a second of theexit pupils of the pair of binoculars.

In accordance with the present invention, there is further provided amethod for providing two spaced-apart parallel light beams at aselectable distance, one of the two spaced-apart parallel light beams isa first datum light beam, the method including establishing a secondlight beam parallel to the first datum light beam based on the firstdatum light beam to create a second datum light beam, wherein the stepfor establishing a second light beam includes receiving an imageresulting from directing the first datum light beam and the second lightbeam through a collimator, if the image is determined to be ofnon-coincidental cast images by the first datum light beam and thesecond light beam, the second light beam is adjusted such that the imagebecomes coincidental with the first datum light beam.

In one embodiment, the method further includes establishing a thirdlight beam parallel to the second datum light beam based on the seconddatum light beam to create a third datum light beam, wherein the stepfor establishing a third light beam includes receiving an imageresulting from directing the second datum light beam and the third lightbeam through a collimator, if the image is determined to be ofnon-coincidental cast images by the second datum light beam and thethird light beam, the third light beam is adjusted such that the imagebecomes coincidental with the second datum light beam. In oneembodiment, the method further includes establishing a fourth light beamparallel to the third datum light beam based on the third datum lightbeam, wherein the parallelity of the fourth light beam is indirectlyestablished with respect to the first datum light beam, wherein the stepfor establishing a fourth light beam includes receiving an imageresulting from directing the third datum light beam and the fourth lightbeam through a collimator, if the image is determined to be ofnon-coincidental cast images by the third datum light beam and thefourth light beam, the fourth light beam is adjusted such that the imagebecomes coincidental with the third datum light beam.

An object of the present invention is to provide a calibration targetfor exit pupils disposed at a large interpupillary distance (IPD).

Another object of the present invention is to provide a passivecalibration target for exit pupils disposed at a large IPD.

Another object of the present invention is to provide an adjustablecalibration target for exit pupils of glasses or binoculars disposed atvarious large IPDs.

Whereas there may be many embodiments of the present invention, eachembodiment may meet one or more of the foregoing recited objects in anycombination. It is not intended that each embodiment will necessarilymeet each objective. Thus, having broadly outlined the more importantfeatures of the present invention in order that the detailed descriptionthereof may be better understood, and that the present contribution tothe art may be better appreciated, there are, of course, additionalfeatures of the present invention that will be described herein and willform a part of the subject matter of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto specific embodiments thereof which are illustrated in the appendeddrawings. Understanding that these drawings depict only typicalembodiments of the invention and are not therefore to be considered tobe limiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a diagram depicting one embodiment of a system for providingcollimated light beams to be supplied to two space-apart exit pupils ofa pair of binoculars for calibration.

FIG. 2 is a diagram depicting one embodiment of a present system forproviding highly-precise two spaced-apart parallel light beams, whereinthe space between the two spaced-apart parallel light beams isconfigured to be adjustable.

FIG. 3 is a diagram depicting one embodiment of a present system forproviding highly-precise two spaced-apart parallel light beams used incalibrating the light paths of a pair of binoculars.

FIG. 4 is a diagram depicting a manner in which the orientation of abeam splitter is corrected.

PARTS LIST

-   2—binocular calibration system-   4—light source-   6—beam splitter-   8—light beam-   10—base-   12—camera-   14—movement-   16—translation mechanism-   18—shutter-   20—image plane-   22—entrance pupil of binoculars-   24—perpendicular distance between two consecutive light beams-   26—cast image-   28—exit pupil-   30—binoculars or binocular telescope-   32—cast image-   34—collimator-   36—reticle-   38—first central axis-   40—second central axis-   42—third central axis-   44—fourth central axis-   46—rotation mechanism-   48—drive gear-   50—driven gear-   52—beam splitter orientation prior to correction-   54—beam splitter orientation after correction-   56—image plane

PARTICULAR ADVANTAGES OF THE INVENTION

The present system is a passive system and does not requireself-monitoring of the parallelity of the two consecutive light beams.As such, the system requires no rotation and/or translation mechanismsthat automatically adjust the orientation and/or position of opticaldevices, e.g., beam splitters. The present system does not require adedicated optical feedback device to ensure that two consecutive lightbeams are parallel. Rather, a calibrated pair of binoculars can be usedto ensure that two consecutive light beams are parallel. As such, thesystem is simpler in its construction and design and requires nocontrollers to detect the lack of parallelity between two light beams.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The term “about” is used herein to mean approximately, roughly, around,or in the region of. When the term “about” is used in conjunction with anumerical range, it modifies that range by extending the boundariesabove and below the numerical values set forth. In general, the term“about” is used herein to modify a numerical value above and below thestated value by a variance of 20 percent up or down (higher or lower).

FIG. 1 is a diagram depicting one embodiment of a system for providingcollimated light beams to be supplied to two space-apart exit pupils 28of a pair of binoculars 30, e.g., a pair of augmented reality/virtualreality (AR/VR) binoculars or a binocular telescope, for calibration. Incalibrating the pair of binoculars 30, a large collimator 34 may be usedto dispose the light beams entering the pair of binoculars through theexit pupils 28 in parallel configuration with the light paths of thebinoculars 30. In this system, in order for the exit pupils 28 to allowimages to traverse the light paths of the binoculars 30 and be cast at acamera 12 disposed at the entrance pupil 22 end of the binoculars 30,the reticle 36 must be visible by the camera 12. A large interpupillarydistance (IPD) necessarily requires the collimator 34 and the reticle 36to be disposed at a large distance from the exit pupils 28 of thebinoculars 30, making the entire setup of the collimator 34 large,costly and impractical due to weight and space limitations of the setup.In addition, if there are binoculars 30 having significantly differentIPDs to be calibrated, multiple sets of collimators 34 and reticles 36may be required, further adding to the costs and setup time. An imageplane 20 or display of camera 12 shows images 26, 32 cast on andreceived by the camera 12. As shown, in order to calibrate the lightpaths of the binoculars 30, adjustments to the light paths must be madeuntil the two cast images 26, 32 of the reticle 36 overlap one another.It is imperative that a calibration setup that is less costly, havingmore compact form factor and higher calibration throughputs be madeavailable to enhance the optical calibration process of a pair ofbinoculars. FIGS. 2-3 depict various aspects of a present calibrationsystem for a pair of binoculars capable for use in calibratingbinoculars having a large range of IPDs without requiring changeouts ofany calibration setups.

FIG. 2 is a diagram depicting one embodiment of a present system forproviding highly-precise two spaced-apart parallel light beams 8,wherein the space between the two spaced-apart parallel light beams 8 isconfigured to be adjustable and the system 2 is configured to be usefulfor calibrating binoculars having vastly different interpupillarydistances (IPDs) or a large range of IPDs. Without a self-monitoringmechanism to ensure that two light beams to be used for calibrating apair of binoculars 30 or to ensure that two light beams have remainedparallel upon adjustment of the perpendicular distance between them tomatch exit pupils of the pair of binoculars, adjustments that span sucha distance must be kept to a minimum, e.g., no more than 90 mm to reducethe risk of causing degradation in parallelity in the two light beams.When the parallelity of two light beams is to be ascertained, the twolight beams must themselves be calibrated, e.g., with a collimator asdisclosed elsewhere herein. Shown in FIG. 2 is essentially oneembodiment of a system 2 useful for providing two parallel light beamsspaced-apart a selectable distance. The system 2 includes, from left toright, a first beam splitter 6, a second beam splitter 6, a third beamsplitter 6 and a fourth beam splitter 6. Combinations of these beamsplitters increase the chance that a necessary perpendicular distancebetween two parallel light beams (to match the IPD of a pair ofbinoculars) can be obtained using a pair of beam splitters to reflectlight from the light source 4. The first beam splitter 6 is configuredfor reflecting a light beam from a light source 4 to create a firstdatum light beam 8, wherein the first datum light beam 6 is configuredto be disposed along a first central axis 38 and the first beam splitter6 is configured to be fixedly attached to a base 10. The second beamsplitter 6 is configured for reflecting a transmitted light beam fromthe light beam from the light source 4 to create a second light beam 8,wherein the second light beam is configured to be disposed along asecond central axis 40 and the second beam splitter 6 is configured tobe slidingly attached to the base 10. The third beam splitter 6 isconfigured for reflecting a transmitted light beam from the light beamfrom the light source 4 to create a third light beam 8, wherein thethird light beam is configured to be disposed along a third central axis42 and the third beam splitter 6 is configured to be slidingly attachedto the base 10. The fourth beam splitter is configured for reflecting atransmitted light beam from the light beam from the light source 4 tocreate a fourth light beam 8, wherein the fourth light beam 8 isconfigured to be disposed along a fourth central axis 44 and the fourthbeam splitter 6 is configured to be slidingly attached to the base 10.The system 2 includes a plurality of light reflecting and transmittingdevices disposed at advantageous distances from one another. Althoughonly a pair of light beams are used at any one IPD calibration activity,more than two light beam reflecting and transmitting devices areprovided to supply two parallel light beams at more than one IPD withoutrequiring a single beam splitter to be adjusted over large distances.Here, there is provided a total of four beam splitters 6 although therightmost beam splitter 6 could be substituted with a mirror instead, asno transmittance by this beam splitter is expected. A full range of IPDscan be cooperatively met by the three sets of light beams. Forsimplicity and clarity in referencing the sets, each light beam has beenassigned a letter “A,” “B,” “C,” or “D” with the leftmost light beamlabelled “A” and the rightmost light beam labelled “D.” As used herein,depending on the context, each letter can refer to the light beam, beamsplitter, mobility mechanism and/or another optical device and/oranother component responsible for generating the light beam associatedwith this letter. Once the parallelity of each light beam with respectto another has been ensured, the AB, AC and AD pairs can be used tocalibrate the parallelity of light paths of a pair of binoculars. InFIG. 2 , a device useful for ensuring the pairs of light beams areparallel, is represented as a collimator 46. As disclosed in FIG. 1elsewhere herein, a single collimator large enough for use to ensure theAD pair of light beams are parallel or even the AC (with a smallerperpendicular distance between the light beams than AD), would beimpractical and costly. In FIG. 2 , only one collimator 46 is used toensure parallelity of AB, BC and CD sequentially although the collimator46 is shown in three positions. In ensuring the parallelity of a pair oflight beams, e.g., AB, images are cast on an image plane, e.g., an imageplane 56, e.g., of a camera through a collimator 34. Parallelity of ABhas been achieved if its light beam B have been adjusted to produce anoverlapped image of cast images 26, 32 due to AB. Once the parallelityof AB has been ensured, B becomes a datum as well with which theparallelity of a subsequent light beam is based. The process of ensuringthat C is parallel with respect to B can be carried out according to theprocess in which the parallelity of B was ascertained with respect to A.Again, once the parallelity of BC has been ensured, C becomes a datum aswell with which the parallelity of a subsequent light beam is based. Theprocess of ensuring that D is parallel with respect to C can be carriedout according to the process in which the parallelity of C wasascertained with respect to B. Once the parallelity of all light beamshas been ensured, any pair of light beams 8 can be used for calibratinga pair of binoculars as shown in FIG. 3 . The system further includesshutters 18 advantageously placed in the plurality of light paths of thesystem to block or allow the respective light beams they control. Forinstance, if only AD are necessary, B and C should be blocked with theirrespective shutters of the second datum light beam, the third datumlight beam and the fourth light beam when the one of the second datumlight beam, the third datum light beam and the fourth light beam is notin use. It can therefore be summarized that a method for providing twospaced-apart parallel light beams at a selectable distance, one of thetwo spaced-apart parallel light beams is a first datum light beam, themethod including establishing a second light beam parallel to the firstdatum light beam based on the first datum light beam to create a seconddatum light beam. The step for establishing a second light beam includesreceiving an image resulting from directing the first datum light beamand the second light beam through a collimator, if the image isdetermined to be of non-coincidental cast images by the first datumlight beam and the second light beam, the second light beam is adjustedsuch that the image becomes coincidental with the first datum lightbeam. In one embodiment, the method further includes establishing athird light beam parallel to the second datum light beam based on thesecond datum light beam to create a third datum light beam. The step forestablishing a third light beam includes receiving an image resultingfrom directing the second datum light beam and the third light beamthrough a collimator, if the image is determined to be ofnon-coincidental cast images by the second datum light beam and thethird light beam, the third light beam is adjusted such that the imagebecomes coincidental with the second datum light beam. In oneembodiment, the method further includes establishing a fourth light beamparallel to the third datum light beam based on the third datum lightbeam, wherein the parallelity of the fourth light beam is indirectlyestablished with respect to the first datum light beam, wherein the stepfor establishing a fourth light beam includes receiving an imageresulting from directing the third datum light beam and the fourth lightbeam through a collimator, if the image is determined to be ofnon-coincidental cast images by the third datum light beam and thefourth light beam, the fourth light beam is adjusted such that the imagebecomes coincidental with the third datum light beam.

FIG. 3 is a diagram depicting one embodiment of a present system forproviding highly-precise two spaced-apart parallel light beams 8 used incalibrating the light paths of a pair of binoculars. Upon ensuring thatthe system can produce two parallel light beams 8 space-apart a suitableperpendicular distance, the light paths of the binoculars 30 can then becalibrated. In use, a pair of binoculars allows light to enter at theentrance pupil end before splitting the image received at the entrancepupil end into two light paths exiting the exit pupils. By the sametoken, in calibrating the light paths of the pair of binoculars, the twoparallelly-disposed light beams supplied at the exit pupils shall resultin a unified image that is an aggregate of the two parallelly-disposedlight beams. Therefore, in calibrating the binoculars, the light pathsof the binoculars are adjusted such that a resulting image at theentrance pupil 22 end is a unified image of the two parallelly-disposedlight beams. In one embodiment, the present system includes a camera 12configured for receiving an image resulting from directing a light beam8 and another light beam 8 through exit pupils 28 of a pair ofbinoculars 30 to an entrance pupil 22 of the pair of binoculars 30 and acontrol device to which the camera 12 is functionally connected and ifthe image is determined to be of non-coincidental cast images 26, 32through the exit pupils 28 of the pair of binoculars 30 by the lightbeam 8 and the other light beam 8, a light path through a first of theexit pupils 28 of the pair of binoculars 30 is determined to be notparallel to a light path through a second of the exit pupils 28 of thepair of binoculars 30. Here, the IPD of the pair of binoculars 30 callsfor the use of AC instead of other combinations, e.g., AB and AD as theadjustments required to bring the perpendicular distance 24 between Aand C to match the IPD of the exit pupils 28 is minimal, significantlyreducing the risk that the parallelity of AC is compromised when theadjustments were made. Translation adjustments along the width of thebase 10 can be made with a translation mechanism 16 that is configuredto make a beam splitter 6 slidingly adjustable along a widthwisedirection of the base 10 with a movement 14 shown in FIG. 2 or FIG. 3 .If rotation correction to a beam splitter 6 is required, it can be madeby way of a rotation mechanism, an example of which is shown elsewhereherein.

FIG. 4 is a diagram depicting a manner in which the orientation of abeam splitter is corrected. Although a rotation mechanism 50 using aplurality of gears 48, 50 is shown, other types of positional ororientational/rotational correction mechanisms may be used. Shown hereinis a beam splitter 6 disposed in an orientation 52 prior to itsorientation correction due to a deviation in the orientation of the beamsplitter 6. Upon correction, the beam splitter is shown disposed inorientation 54. Here, a drive gear 52 is used to correct the orientationof the beam splitter by driving the driven gear 54 attached to the beamsplitter 6 such that a rotation of the drive gear 52 results in arotation of the beam splitter 6 and the driven gear 54 in unison. In oneembodiment, the cast images, e.g., B, A are cast images of light spotsand/or reticles 36 to ensure that completion of a correction process forbringing a light beam into parallelity with a datum light beam can beeasily discerned. Referring back to FIG. 2 , non-parallelity of twolight beams causes the two light beams to appear as light spots A, B, C,D or reticles if reticles are used. For example, the paralellity oflight beam B that is translated and/or rotated or otherwise correctedwith respect to datum light beam A can be said to have achievedparallelity with datum light beam A when the cast images B, A overlapone another. Referring back to FIG. 3 , calibration of the light pathsof the binoculars may be accomplished manually. In a manual process, thelight paths of the binoculars are adjusted manually until the castimages 26, 32 are observed to overlap one another. A requirement forcalibration of the light paths of the binoculars originates from thedetermination that the cast images 26, 32 do not overlap. The lightpaths of the binoculars are adjusted and another determination ofwhether the cast images 26, 32 approach one another is made. If they do,continue the adjustments until the cast images 26, 32 overlap. If theydepart from one another, reverse the adjustments until the cast images26, 32 overlap.

The detailed description refers to the accompanying drawings that show,by way of illustration, specific aspects and embodiments in which thepresent disclosed embodiments may be practiced. These embodiments aredescribed in sufficient detail to enable those skilled in the art topractice aspects of the present invention. Other embodiments may beutilized, and changes may be made without departing from the scope ofthe disclosed embodiments. The various embodiments can be combined withone or more other embodiments to form new embodiments. The detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims,with the full scope of equivalents to which they may be entitled. Itwill be appreciated by those of ordinary skill in the art that anyarrangement that is calculated to achieve the same purpose may besubstituted for the specific embodiments shown. This application isintended to cover any adaptations or variations of embodiments of thepresent invention. It is to be understood that the above description isintended to be illustrative, and not restrictive, and that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Combinations of the above embodimentsand other embodiments will be apparent to those of skill in the art uponstudying the above description. The scope of the present disclosedembodiments includes any other applications in which embodiments of theabove structures and fabrication methods are used. The scope of theembodiments should be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled.

What is claimed herein is:
 1. A method for providing two spaced-apartparallel light beams at a selectable distance, one of the twospaced-apart parallel light beams is a first datum light beam, saidmethod comprising establishing a second light beam parallel to the firstdatum light beam based on said first datum light beam to create a seconddatum light beam, wherein said step for establishing a second light beamparallel to the first datum light beam comprises receiving an imageresulting from said first datum light beam and said second light beamdirected through a collimator and a pair of binoculars, if said image isdetermined to be of non-coincidental cast images by said first datumlight beam and said second light beam, said second light beam isadjusted such that said cast image of said second light beam becomescoincidental with said cast image of said first datum light beam.
 2. Themethod of claim 1, further comprising establishing a third light beamparallel to said second datum light beam based on said second datumlight beam to create a third datum light beam, wherein said step forestablishing a third light beam parallel to said second datum light beamcomprises receiving an image resulting from said second datum light beamand said third light beam directed through the collimator and the pairof binoculars, if said image is determined to be of non-coincidentalcast images by said second datum light beam and said third light beam,said third light beam is adjusted such that said cast image of saidthird light beam becomes coincidental with said cast image of saidsecond datum light beam.
 3. The method of claim 2, further comprisingestablishing a fourth light beam parallel to said third datum light beambased on said third datum light beam to create a fourth datum lightbeam, wherein said step for establishing a fourth light beam parallel tosaid third datum light beam comprises receiving an image resulting fromsaid third datum light beam and said fourth light beam directed throughthe collimator and the pair of binoculars, if said image is determinedto be of non-coincidental cast images by said third datum light beam andsaid fourth light beam, said fourth light beam is adjusted such thatsaid cast image of said fourth light beam becomes coincidental with saidcast image of said third datum light beam.